Control of RNA polymerase II (Pol II) activity is the major mechanism underlying cellular differentiation during development. For some genes, this includes regulation at the level of transcription elongation. The mammalian Pol II elongation factor ELL is distinguished as being able to increase the catalytic rate of Pol II in vitro. ELL homologs are absent from yeast, suggesting that the ELL family of elongation factors represents an adaptation of metazoans. The long-term goal of this project is to understand the role of the ELL family of transcription elongation factors in the regulation of gene expression. The Drosophila homolog of ELL (dELL) broadly co-localizes with phosphorylated Pol II on polytene chromosomes, is concentrated at sites of active transcription and is associated with Pol II in whole fly extracts. Mutations in the dELL coding sequence are found in independently isolated mutant alleles of Suppressor of triplo-lethal [Su(Tpl)]. Su(Tpl) is an essential gene, and the phenotypes of Su(Tpl) mutations are consistent with a defect in a general transcription factor. dELL is the only ELL-family protein in flies. This project will test whether dELL functions in transcription in living cells, and what role it plays in regulating gene expression. Specific Aim 1 will test whether dELL is recruited to the body of transcribing genes in vivo. Specific Aim 2 will test whether dELL is limiting for gene transcription in vivo. The expression of various patterning genes will be tested in early embryos in which dELL has been inactivated by RNAi, to see whether loss of dELL results in their down-regulation. Specific Aim 3 will test the ability of a dELL transgene to complement the recessive lethality of Su(Tpl) mutations, and whether a truncated dELL transgene behaves as a dominant negative on a wild-type background. These studies will provide the first detailed understanding of the role for the ELL-family of proteins and their gene expression in vivo. They will also provide the foundation for a genetic dissection of dELL and for understanding the regulation of Pol II in development.
